With increase in the Arctic warming, fjords in the region are undergoing significant decline in sea-ice, increase in glacier retreat, and changes in primary productivity. Warm and saline Atlantic water (AW) advected from the open ocean is attributed as one of the primary reasons for these changes. Vertical mixing of the subsurface AW with the cold surface Arctic water positively feeds many of these changes. One of the major contributors of vertical mixing in the water column is the near-inertial waves (NIW). In this study, we report prominent NIW activity in Kongsfjorden, an Arctic fjord in west Svalbard, using hydrography observations and numerical simulations. Shallow summer mixed layer depth facilitates generation of strong near-inertial currents in the mixed layer (ML), even with relatively weak storms. During storm events in summer, the near-inertial currents induce large shear at the base of the ML and downward propagating NIW induce shear in the fjord interior leading to an enhanced vertical mixing. These two processes during summertime storms lead to redistribution of the subsurface AW thereby warming the ML. Numerical simulations from the Regional Ocean Modelling System (ROMS) are used to understand the generation, dissipation and energetics of the NIW and their impact on vertical mixing in the fjord. Near-inertial energy budget estimations show that $\sim$45% of near-inertial energy input in the fjord and continental shelf–slope region dissipates within the upper 150 m of the water column. Numerical experiments are performed to confirm the role of storms in inducing vertical mixing of the AW. When storms are removed from the forcing field, eddy diffusivity reduces and fails to reproduce the upper ocean warming that was present in the simulation with storms. Even though stability in the fjord upper layer is enhanced with an increased glacier discharge, strong vertical mixing is still profound during storms. Consistent with this, in the experiment with double the glacier discharge, near-inertial energy flux increases by nearly 10% whereas the viscous dissipation of the NIW increases by about 13%. The findings of the study underscore the potential significance of the NIW dynamics and their impacts in the Arctic fjords. This is further relevant in understanding the vertical mixing in shallow regions such as shelves, slopes and fjords in the future Arctic with more storms and reduced sea-ice cover as projected by climate models.

随着北极变暖的加剧，该地区的峡湾正在经历海冰的显着减少、冰川退缩的增加以及初级生产力的变化。从公海平流的温暖的咸大西洋水（AW）被认为是这些变化的主要原因之一。地下 AW 与北极寒冷地表水的垂直混合对许多这些变化起到了积极的推动作用。水柱中垂直混合的主要贡献者之一是近惯性波（NIW）。在这项研究中，我们使用水文观测和数值模拟报告了在西斯瓦尔巴群岛的北极峡湾 Kongsfjorden 的突出 NIW 活动。浅的夏季混合层深度有利于在混合层 (ML) 中产生强烈的近惯性流，即使风暴相对较弱。在夏季的风暴事件中，近惯性流在 ML 底部引起大剪切，向下传播的 NIW 在峡湾内部引起剪切，导致垂直混合增强。夏季风暴期间的这两个过程导致地下 AW 的重新分布，从而使 ML 变暖。区域海洋建模系统 (ROMS) 的数值模拟用于了解 NIW 的产生、耗散和能量学及其对峡湾垂直混合的影响。近惯性能量预算估计表明，区域海洋建模系统 (ROMS) 的数值模拟用于了解 NIW 的产生、耗散和能量学及其对峡湾垂直混合的影响。近惯性能量预算估计表明，区域海洋建模系统 (ROMS) 的数值模拟用于了解 NIW 的产生、耗散和能量学及其对峡湾垂直混合的影响。近惯性能量预算估计表明，$～$峡湾和大陆架斜坡区 45% 的近惯性能量输入在水柱上部 150 m 内消散。进行数值实验以确认风暴在诱导 AW 垂直混合中的作用。当风暴从强迫场中移除时，涡流扩散率降低并且无法再现风暴模拟中存在的上层海洋变暖。尽管峡湾上层的稳定性随着冰川流量的增加而增强，但在风暴期间，强烈的垂直混合仍然很严重。与此一致，在冰川放电加倍的实验中，近惯性能量通量增加了近 10%，而 NIW 的粘性耗散增加了约 13%。该研究的结果强调了 NIW 动态的潜在意义及其对北极峡湾的影响。这对于理解未来北极地区（如气候模型预测的更多风暴和减少的海冰覆盖）在大陆架、斜坡和峡湾等浅层区域的垂直混合具有进一步的相关性。